1. Field of the Invention
This invention relates to an optical unit in which an optical element, such as a mirror, and an actuator for making its positioning control are integrally constructed, and in particular, to an optical unit suitable for fabrication with the use of a semiconductor manufacturing technique.
2. Description of the Related Art
A technique that an optical element, such as a mirror, a lens, a diffraction grating, or a pinhole plate, is controlled by an actuator so that its direction and position are changed has long been known. In recent years, however, it is a common practice to fabricate the optical element and the actuator as a unit. In particular, for an optical unit incorporated in a small-sized electronic device, the semiconductor manufacturing technique has come into prominent use for fabrication. A conventional example of such an optical unit fabricated by using the semiconductor manufacturing technique is disclosed in Japanese Patent Kokai No. Hie 8-322227.
This conventional example uses a gimbal structure so that a mirror is displaced by the torsional function of a torsion bar. As such, it has the feature that a two-dimensional tilt displacement is achieved on the optical path with respect to the mirror and a scan can be performed with reflected light. Since, as mentioned above, the optical unit can be fabricated by using the semiconductor manufacturing technique, this is advantageous for compactness of the unit. Furthermore, an electromagnetic driving system is used, and thus a low-voltage drive is possible.
Although the conventional example is capable of performing the tilt displacement of the mirror on the optical path, no account is taken of the technique that the mirror is caused to rest at an arbitrary tilting position, and this technique is basically difficult in structure. When the conventional example is designed so that the whole of the mirror can also be displaced in a vertical direction (along the optical axis of incident light), a longer torsion bar must be provided. This not only requires a greater driving force, but also causes oversizing of the unit, and there is the problem that the optical unit has no practical use. Moreover, the conventional example, which is of the electromagnetic driving system, has the structure that a large number of parts, such as permanent magnets, are basically required, which is disadvantageous for compactness and cost reduction. Although a driving voltage is low, power consumption is somewhat increased, and thus there is a case where it is not necessarily electrically advantageous.
In an optical apparatus such as a digital camera, for focusing, zoom, and shake prevention, motors and solenoids have been used as driving sources of driving means for displacing optical elements constituting an optical system with respect to their functions, and the displacements of the optical elements have been controlled by mechanical means such as gears and cams.
Specifically, the motors and mechanical means must be driven in accordance with focusing and zoom, and hence power consumption is increased. In addition, since the mechanical means, such as gears, provided to displace the optical elements must be started for operation and stopped, response time is long. Furthermore, optical performance cannot be achieved with a high degree of accuracy because of the error of backlash of the mechanical means.